This invention relates generally to indexing systems of machines such as lathes and other machine tools. More particularly, the invention relates to an indexing system having a relatively simple construction which is capable of holding a driven structure which has been indexed with a positive mechanical locking action against heavy loads so that its definitely determined indexed position will not shift unintentionally and, moreover, is capable of operating positively with the driven structure moving at high speed.
Indexing systems and devices are widely used in machining operations. Each indexing system and the machine in which it is installed require a certain indexing time for each indexing operation. The shorter this indexing time is, the longer will the effective machining time be. For this reason, in order to elevate productive efficiency, there has been a great demand for high-speed indexing.
As one example, the indexing of the turret of a numerically controlled (NC) lathe will be considered. Heretofore, the most common indexing process has comprised, with the use of a clutch coupling, the sequential steps of (a) raising of the turret head to disengage a clamp of the coupling, (b) rotation of a turret indexing mechanism to carry out indexing of the turret head, and (c) retraction and clamping of the turret head simultaneously with completion of the indexing of the turret head.
A mechanism for carrying out this operation is that, for example, disclosed in Japanese Utility Model Laid Open Publication No. 57-202608 (202608/1982) and described more fully hereinafter. In this mechanism, briefly stated, a pin wheel driven by a motor carries out indexing of a turret via a geneva mechanism, while a cam also driven by the motor simultaneously accomplishes engagement or disengagement of a clutch coupling between the turret and the frame structure. This mechanism, however, has a disadvantageously complicated construction and high production cost due to the requirement of high dimensional precision in the fabrication of the cam for accurate, rapid, and cooperative movements in above described operational steps (a), (b), and (c).
Furthermore, when this mechanism is applied to an NC lathe for heavy turning work, it is necessary to withstand a heavy load to hold the engagement of the coupling. While a mechanical force afforded by a pin acts during the disengagement of the coupling at the time of indexing in this mechanism, the engagement force depends on the elastic force of a spring. For this reason, a spring of great spring force must be used. As a consequence, the cam and other parts of the engaging and disengaging mechanism of the coupling must unavoidably be made strong and large, whereby high-speed rapid operation cannot be attained, and moreover, a further increase in the cost arises.